Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) catalyst to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3). Generally in such conventional aftertreatment systems, an exhaust reductant, (e.g., a diesel exhaust fluid such as urea) is injected into the aftertreatment system to provide a source of ammonia, and mixed with the exhaust gas to partially reduce the NOx gases. The reduction byproducts of the exhaust gas are then fluidically communicated to the catalyst included in the SCR aftertreatment system to decompose substantially all of the NOx gases into relatively harmless byproducts which are expelled out of such conventional SCR aftertreatment systems.
An exhaust reductant is generally inserted into SCR system as the source of ammonia to facilitate the reduction of constituents of the exhaust gas (e.g., a diesel exhaust gas). The exhaust reductant is stored in a reductant storage tank and communicated to the SCR system. Presence of an improper reductant in the storage tank (e.g., an incorrect reductant, or an incorrect concentration of an exhaust reductant such as urea in an aqueous solution) negatively impacts the SCR catalyst catalytic conversion efficiency. However, catalytic conversion efficiency is also negatively impact by a degraded catalyst.
In conventional aftertreatment systems, an exhaust reductant storage tank level sensor that detects a sudden change in the level of the exhaust reductant is generally also used to indicate the presence of an improper reductant in the exhaust reductant storage tank. However, the tank level sensor provides an inaccurate assessment of the exhaust reductant. Thus, reduction of SCR catalytic conversion efficiency due to improper reductant is often inaccurately attributed to degradation of the catalyst of the SCR system. Replacing the catalyst is substantially more expensive than replacing the improper reductant. Therefore, incorrect diagnosis leads to unnecessary maintenance expenses substantially driving up the cost for maintaining aftertreatment systems.